[오타수정] Part 2. Window size and scrolling

## 원문
Part 2. 1.10 - Window sizes and scrolling 중

## 오타수정
elem.scrollLeft/scrollTop -> element.scrollLeft/scrollTop
## 이슈
elem보다 element로 수정하는 것이 보는 사람들로 하여금 혼동을 덜 줄 것 같습니다.

## Pull Request(PR)를 통해 수정할 의향이 있습니까?
Yes

Open Part 2, section 1.10, “Window sizes and scrolling,” in the Korean tutorial and inspect the text shown in the referenced image. Change `elem.scrollLeft/scrollTop` to `element.scrollLeft/scrollTop`, then verify the rendered section uses the clearer terminology throughout.

Written by the indexing model from the issue text.